Syndiotactic 1,2-polybutadiene polymer is crystalline thermoplastic resin that has a stereoregular structure in which the side chain vinyl 1,2- groups are located alternately on opposite sides in relation to the polymeric main chain. Syndiotactic 1,2-polybutadiene is a unique polymeric material what exhibits various physical properties of both plastics and rubber and, therefore, has many uses. For example, syndiotactic 1,2-polybutadiene can be beneficially blended with various diene-based elastomers for use in various articles of manufacture, including tires having one or more components thereof.
Syndiotactic 1,2-polybutadiene may be prepared, for example, by polymerizing 1,3-butadiene monomer in an organic solvent solution in the presence of a catalyst system containing a trialkylaluminum, a cobalt carboxylate and carbon disulfide. For example, see U.S. Pat. No. 3,778,424 for preparation of syndiotactic 1,2-polybutadiene polymer. See also U.S. Pat. Nos. 5,307,850 and 5,283,294 for preparation of a composite of conjugated diene-based elastomer and syndiotactic 1,2-polybutadiene polymer.
However use of the volatile carbon disulfide in such catalyst system presents a challenge in a sense because of its inherently relatively obnoxious odor.
For this invention, the preparation of syndiotactic 1,2-polybutadiene in an organic solvent solution in the presence of a carbon disulfide-containing catalyst system is made more environmentally acceptable in a sense of a significantly reduced obnoxious odor associated with such use.
For the description of this invention, the term “polymerizate” means a polymerization reaction medium comprised of an organic solvent solution of polymerized monomers (e.g. isoprene and 1,3-butadiene) and an accompanying live catalyst system.
Disclosure and Practice of the Invention
In accordance with this invention, in a process is provided for the preparation of syndiotactic 1,2-polybutadiene polymer which comprises polymerizing 1,3-butadiene in an organic solvent solution in the presence of a catalyst system comprised of a combination of cobalt carboxylate, trialkyl aluminum, carbon disulfide and, optionally dialkylfumarate, to form a polymerizate thereof and thereafter recovering said syndiotactic 1,2-polybutadiene from said polymerizate;                wherein said process further comprises adding hydrogen peroxide to said polymerizate.        
As would be understood by one having skill in such art, at least a stoichiometric amount of the hydrogen peroxide would be used relative to said carbon disulfide and preferably a reasonable excess over and above such stoichiometric amount and, further that the hydrogen peroxide be preferably added at a temperature in a range of about, for example, 23° C. to about 50° C. to oxidize the organic sulfide(s) to, for example sulfoxides and/or sulfates.
While the hydrogen peroxide is the preferred oxidizing agent for this invention based on cost, efficiency and availability without leaving its residue in the resulting product, other less advantageous oxidizing agents might possibly be considered but which may leave residues such as for example, potassium permangenate (may leave manganese residue which may be difficult and costly to remove), as well as chlorine gas (which may be toxic and may change the composition of the resulting product), and potassium perchlorate.
In practice, the said addition of hydrogen peroxide may be added to said polymerizate as a mixture comprised of hydrogen peroxide and water and/or alcohol, preferably alcohol, wherein said alcohol comprised of at least one of ethanol and isopropanol.
In further accordance with this invention, a syndiotactic 1,2-polybutadiene polymer prepared by said process is provided.
In additional accordance with this invention, a tire is provided which contains at least one component comprised of a rubber composition which contains said syndiotactic 1,2-butadiene polymer.
It is considered herein that said hydrogen peroxide reacts with said carbon disulfide, particularly unreacted carbon disulfide, which may include one or more byproducts of said carbon disulfide thereof, to significantly reduce the level (essentially eliminating the level) of obnoxious odor which would otherwise be stemming from said carbon disulfide (e.g. unreacted carbon disulfide).
It is considered herein that said hydrogen peroxide also acts to inactivate said catalyst system and stop said polymerization reaction.
Alternatively, when said hydrogen peroxide is added as a solution comprised of water and/or said alcohol water and/or alcohol also acts to inactivate said catalyst system to stop said polymerization reaction to therefore prevent further formation of said polymerizate.
In practice, said cobalt carboxylate may be, for example, selected from cobalt octanoate, cobalt naphthenate and cobalt acetylacetonate, preferably cobalt octanoate.
In practice, said trialkylaluminum may be, for example, selected from triethylaluminum and triisobutylaluminum, preferably triisobutylaluminum.
In practice, said optional dialkyl fumarate may be, for example, selected from dimethyl fumarate, diethyl fumarate and dibutyl fumarate, preferably diethyl fumarate.
Accordingly, said catalyst system may be, for example, comprised of the product of a combination of cobalt naphthenate, triisobutyl aluminum and carbon disulfide as well as, optionally, diethyl fumarate.
A significant aspect of this invention is the aforesaid addition of the simple hydrogen peroxide, preferably in said simple alcohol solution thereof, for aforesaid reaction with said carbon disulfide and perhaps also with byproducts of said carbon disulfide.
Such significant aspect of the invention is amplified by an inclusion of the use of the dialkylfumarate in the catalyst system combination which, in turn allows the reduced amount of the carbon disulfide in the catalyst system combination to effectively polymerize the 1,3-butadiene to form the syndiotactic 1,2-polybutadiene polymer and to thereby further reduce obnoxious odor stemming from the carbon disulfide.
In practice, various acceptable inert organic solvents may be used for said polymerization, representative of which are, for example, hexane, pentane, cyclohexane and toluene.
The polymerization may be conducted, for example, at atmospheric pressure or above atmospheric pressure.
The polymerization may be conducted, for example, at a constant temperature or variable temperature in a range of, for example, from about 0° C. to about 60° C.
In a further accordance with this invention, a process comprises preparing a composite of conjugated diene-based elastomer and syndiotactic 1,2-polybutadiene polymer comprised of first polymerizating at least one of isoprene and 1,3-butadiene monomers, or styrene and at least one of isoprene and butadiene monomers, in an organic solvent solution to form a polymerizate containing an elastomer thereof followed an addition of 1,3-butadiene monomer and said catalyst comprised of said trialkyl aluminum, cobalt carboxylate and carbon disulfide, and optionally said dialkyl fumarate, and polymerizing said added 1,3-butadiene to form a syndiotactic 1,2-polybutadiene polymer, wherein the resulting polymerizate of said conjugated diene-based elastomer and syndiotactic 1,2-polybutadiene polymer is treated with hydrogen peroxide, followed by recovering said composite from said polymerizate.
In practice, then, said conjugated diene-based elastomer of said composite may be, for example, cis 1,4-polyisoprene, cis 1,4-polybutadiene, isoprene/butadiene copolymer, styrene/isoprene/butadiene terpolymer or styrene/butadiene copolymer.
It is considered herein that said hydrogen peroxide treatment of said polymerizate renders it relatively odorless insofar as a significant level of obnoxious odor stemming from said carbon disulfide is concerned.
Said composite (hydrogen peroxide treated composite) of said conjugated diene-based elastomer and syndiotactic 1,2-butadiene polymer is then recovered from said polymerizate.
It is considered herein that said hydrogen peroxide treatment of said polymerizate renders said recovered composite relatively odorless insofar as a significant level of obnoxious odor stemming from said carbon disulfide is concerned.
In additional accordance with this invention, said composite of conjugated diene-based elastomer and syndiotactic 1,2-polybutadiene polymer prepared by said process is provided.
In further accordance, a rubber composition is provided containing said composite of conjugated diene-based elastomer and syndiotactic 1,2-polybutadiene polymer is provided, particularly as prepared by the process of this invention (e.g. a rubber composition comprised of said composite, at least one additional conjugated diene-based elastomer and reinforcing filler such as for example rubber reinforcing fillers comprised of at least one of rubber reinforcing carbon black and precipitated silica and any combination of the two reinforcing fillers).
In additional accordance with this invention, a tire is provided which contains at least one rubber component comprised of a rubber composition which contains said syndiotactic 1,2-polybutadiene copolymer prepared by the process of this invention. (e.g. which also contains at least one additional conjugated diene-based elastomer and reinforcing filler comprised of at least one of rubber reinforcing carbon black and precipitated silica together with a coupling agent for said precipitated silica).
In additional accordance with this invention, a tire is provided which contains at least one rubber component comprised of a rubber composition which contains said composite of conjugated diene-based elastomer and syndiotactic 1,2-butadiene polymer, particularly as prepared by the process of this invention. (e.g. which also contains at least one additional conjugated diene-based elastomer and reinforcing filler comprised of at least one of rubber reinforcing carbon black and precipitated silica together with a coupling agent for said precipitated silica).
It is to be appreciated that said tire rubber component may be, for example, a tire tread, tire sidewall, internal tire sidewall apex and internal tire sidewall insert particularly as being spaced apart from a tire bead component.
The invention may be better understood by reference to the following example in which the parts and percentages are by weight unless otherwise indicated.